Engine knock is an undesirable condition or operating state of an engine. In many situations, the engine operates most efficiently with incipient engine knock. Nevertheless, excessive engine knock can internally damage the engine.
The operating state of an engine can be monitored to detect engine knock. From the engine, indirect external operating conditions can be sensed by instrumentation, such as accelerometers and acoustic sensors, for outputting measurement signals in response thereto. Also, direct internal operating conditions can be sensed by instrumentation such as a cylinder pressure sensor for outputting measurement signals in response thereto.
At a fundamental characteristic frequency, such direct and indirect measurement signals can indicate the presence of engine knock by exceeding a threshold amplitude. Such a characteristic frequency can vary according to different engine configurations. For a given engine configuration, a characteristic frequency is relatively stable over the entire operating range of the engine.
According to one previous technique, a set of measurement signals is filtered by an analog bandpass filter to isolate measurement signals around a fundamental characteristic frequency. A processor analyzes the isolated measurement signals to determine whether a threshold amplitude is exceeded at the characteristic frequency. Typically, such a technique results in limited system performance by failing to suitably analyze a particular set of filtered measurement signals at multiple characteristic frequencies. Frequently, hardware size and system cost are undesirably increased by including additional analog bandpass filters. Moreover, such a technique is frequently difficult to implement and adapt for variations in process parameters such as characteristic frequency and pass band.
According to another previous technique, a digital bandpass filter isolates measurement signals around a characteristic frequency. As the levels of frequency selectivity and resolving power increase, such a technique can result in decreased system throughput, increased memory requirements, and increased computational intensity. Moreover, such a technique is frequently difficult to adapt for variations in process parameters such as measurement signal set size, sample rate, characteristic frequency and pass band.
In yet another previous technique, the set of measurement signals is processed according to a digital fast Fourier transform ("FFT"). Typically, a single FFT undesirably involves all frequency components of a set of measurement signals, resulting in decreased system throughput, increased memory requirements, and increased computational intensity.
Thus, a need has arisen for a method and system for monitoring an operating state of an engine, in which system throughput is increased relative to previous techniques. Also, a need has arisen for a method and system for monitoring an operating state of an engine, which are more readily implemented and adapted for variations in process parameters relative to previous techniques. Further, a need has arisen for a method and system for monitoring an operating state of an engine, in which a particular set of measurement signals is suitably analyzed at multiple characteristic frequencies. Moreover, a need has arisen for a method and system for monitoring an operating state of an engine, in which a particular combination of hardware size, system cost, and performance is more readily improved relative to analog bandpass electronic circuitry techniques for given levels of frequency selectivity and resolving power. Finally, a need has arisen for a method and system for monitoring an operating state of an engine, in which memory requirements and computational intensity are decreased relative to FFT techniques and digital bandpass filter techniques for given levels of frequency selectivity and resolving power.